An organic EL element is formed on a light-transmitting substrate by stacking sequentially a light-transmitting electrode layer, an organic layer containing an organic electroluminescent substance and an electrode layer that may or may not have light transmission. Also, an organic EL lighting device having a plurality of organic EL elements arranged in a row on plane is a planar thin film light source having high utilization since it emits light at a low voltage and responses in a high speed. Such an organic EL lighting device allows light emitted from the organic layer of organic EL element to transmit the light-transmitting electrode layer and the light-transmitting substrate so as to direct to an exterior.
In such an organic EL element, generally a light-transmitting electrode layer is a positive electrode formed from a material having light transmittance such as indium tin oxide (ITO), zinc oxide or tin oxide, and an electrode layer that may or may not have light transmittance is a negative electrode formed from a metallic thin film or the like. The materials used for the light-transmitting electrode layer have a high specific resistance. Therefore, if these materials are formed as a thin film electrode layer, sheet resistance (surface resistivity) and wiring resistance are large. As a result, non-uniform brightness is caused at a region away from a power supply terminal of the light-transmitting electrode layer. This is because the organic EL element emits light by electric field impression. Since an electric field is decreased due to voltage drop at a central portion of the light-transmitting electrode layer away from a power supply terminal, the efficiency of carrier injection is reduced and then light emission is reduced. To solve this problem, an auxiliary electrode is installed on the light-transmitting electrode layer to suppress the reduction of resistance at a region away from a power supply terminal. Since such an auxiliary electrode has a light-blocking property, it is formed by patterning on portions of a surface of the light-transmitting electrode layer. Further, due to suppressing conduction piercing through an organic layer between the auxiliary electrode and the electrode layer formed from a metallic thin film or the like, the auxiliary electrode is coated with a polymer insulating coating film. If the auxiliary electrode is formed from aluminum or silver that allows the light-transmitting electrode layer to have a reduced resistivity, defects in layer structure such as vacancies or voids are generated at an atomic structure level due to electromigration or stressmigration and stability is lowered. Therefore, such an auxiliary electrode is formed from chromium or molybdenum having high stability to operation.
However, an auxiliary electrode formed from chromium or molybdenum, which is suppressed in electromigration or stressmigration and has excellent stability and reliability, an effect of auxiliary electrode that allows a light-transmitting electrode layer to have a reduced resistivity may be insufficient. Further, there is the problem of environment pollution in using chromium or the like.
As organic EL lighting devices which are suppressed in voltage drop at a central portion of a light-transmitting electrode layer, it has been known an organic EL display in which an auxiliary wiring of In, Pb, Sn, In-based alloy or the like is installed on a transparent electrode such as ITO and the efficiency of light emission is 11 m/W or more (Patent document 1), or an organic EL panel in which a rhombic frame-shaped auxiliary electrode is installed between a transparent electrode and an organic light-emitting layer and a power supply terminal unit is installed within the auxiliary electrode to suppress the reduction of brightness (Patent document 2).
Additionally, it has been known an organic EL display having a plurality of displaying regions (organic ELs) in which any one of first and second wirings disposed within each displaying region is stacked on a connection wiring between one displaying region and another displaying region, i.e. in regions without a light-emitting layer including organic ELs, wherein the connection wiring is formed from a material such as Al which has sheet resistance lower than those of first and second wirings, whereby suppressing an increase in wiring electric resistance due to a lengthened wiring (Patent document 3), or a semiconductor device in which a low resistivity metal such as aluminum neodymium alloy (a second metal layer) is coated with molybdenum having a high melting point (a first metal layer) in a intersecting region among a signal line of low resistivity metal such as aluminum neodymium alloy, a power source control line and an scanning line, whereby preventing the generation of a heat hillock of aluminum neodymium alloy due to laser scanning (Patent document 4).